Method, system, and device for heating a phase change memory (pcm) cell

ABSTRACT

Embodiments disclosed herein may relate to heating a phase change memory (PCM) cell.

BACKGROUND

1. Field

Subject matter disclosed herein may relate to integrated circuitdevices, and may relate, more particularly, to memory devices.

2. Information

Integrated circuit devices, such as memory devices, for example, may befound in a wide range of electronic devices. For example, memory devicesmay be used in computers, digital cameras, cellular telephones, personaldigital assistants, etc. Factors related to a memory device that may beof interest in considering suitability for any particular applicationmay include, physical size, storage density, operating voltages,granularity of read/write operations, throughput, transmission rate,and/or power consumption, for example. Other example factors that may beof interest may include cost of manufacture, and/or ease of manufacture.

BRIEF DESCRIPTION OF THE DRAWINGS

Claimed subject matter is particularly pointed out and/or distinctlyclaimed in the concluding portion of the specification. However, both asto organization and/or method of operation, together with objects,features, and/or advantages thereof, it may best be understood byreference to the following detailed description if read with theaccompanying drawings in which:

FIG. 1 is an illustration depicting an isometric view of an exampleapparatus including a phase change memory (PCM) cell according to anembodiment.

FIG. 2 is a graph in which resistivity is plotted against temperaturefor a memory material that may be utilized in a PCM cell according to anembodiment.

FIG. 3 is an illustration depicting an isometric view of another exampleapparatus including a phase change memory (PCM) cell according to anembodiment.

FIG. 4 is an illustration depicting an isometric view of yet anotherexample apparatus including a phase change memory (PCM) cell, accordingto an embodiment.

FIG. 5 is an illustration depicting an isometric view of another exampleapparatus including a phase change memory (PCM) cell, according to anembodiment.

FIG. 6 is a schematic block diagram depicting a system which may includea PCM device according to an embodiment.

Reference is made in the following detailed description to theaccompanying drawings, which form a part hereof, wherein like numeralsmay designate like parts throughout to indicate corresponding and/oranalogous components. It will be appreciated that components illustratedin the figures have not necessarily been drawn to scale, such as forsimplicity and/or clarity of illustration. For example, dimensions ofsome components may be exaggerated relative to others. Further, it is tobe understood that other embodiments may be utilized. Furthermore,structural and/or functional changes may be made without departing fromthe scope of claimed subject matter. It should also be noted thatdirections and/or references, for example, such as up, down, top,bottom, and so on, may be used to facilitate discussion of drawingsand/or are not intended to restrict application of claimed subjectmatter. Therefore, the following detailed description is not to be takento limit the scope of claimed subject matter and/or equivalents.

DETAILED DESCRIPTION

Integrated circuit devices, such as non-volatile memory devices, may befound in a wide range of electronic devices. Non-volatile memory devicesmay be used in computers, digital cameras, cellular telephones, and/orpersonal digital assistants, to name but a few examples. Factors relatedto a non-volatile memory device that may be of interest in consideringsuitability for a particular application may include physical size,storage density, operating voltages, granularity of read/writeoperations, throughput, transmission rate, cost of manufacture, and/orease of manufacture, for example. Other example aspects that may be ofinterest in considering suitability for a particular application mayinclude power consumption and/or programming voltage and/or current. Anexample type of non-volatile memory device may comprise a phase changememory (PCM) device, in an embodiment.

FIG. 1 is an illustration depicting an isometric view of an exampleapparatus 100 that may include a phase change memory (PCM) cell, such as120, according to an embodiment. Apparatus 100 may comprise memory cell120, a “top” electrode 110, and a “bottom” electrode 130. It should benoted that directions and/or references, for example, such as up, down,top, bottom, and so on, may be used to facilitate discussion of drawingsand/or are not intended to restrict application of claimed subjectmatter. However, it is noted that for the embodiment illustrated,current may flow from electrode 130 to electrode 110 during programmingof the cell, for example, although claimed subject matter is not limitedin scope in this respect. In another embodiment, current may flow in adifferent direction, for example.

A portion of an electrically conductive component 140 is also depictedin FIG. 1. In an embodiment, an electrically conductive component, suchas electrically conductive component 140, may comprise a component thatmay be utilized to route electrical signals and/or power within a memoryarray, for example. An electrically conductive component, such as anelectrically conductive component 140, may comprise a sufficientlyelectrically conductive material, such as polysilicon, carbon, and/ormetallic material, such as tungsten, titanium nitride, and/or titaniumaluminum nitride, for example, for use in a memory device. Of course,claimed subject matter is not limited in scope in these respects. Othermaterials may, of course, also be used in an embodiment. Also in anembodiment, top electrode 110 may comprise a sufficiently electricallyconductive material, such as polysilicon, carbon, and/or metallicmaterial, such as tungsten, titanium nitride, and/or titanium aluminumnitride, for example, for use in a memory device, although again claimedsubject matter is not limited in scope in these respects.

In an embodiment, cell 120 may comprise a memory material, such as achalcogenide glass material. A PCM cell, such as 120, may comprise amemory material capable of storing one or more of at least two differentselectable states to thereby operate as a memory. For example, in abinary system, states may be considered a binary “0” or a binary “1.” Inan embodiment, a “set” state, representing a binary value of ‘1,’ forexample, may correspond to a more crystalline, more conductive state formemory material of a PCM cell, such as 120. Also, in an embodiment, a“reset” state, representing a binary value of ‘0,’ for example, maycorrespond to a more amorphous, more resistive state of a memorymaterial for a PCM cell, such as 120. Of course, assignment of states toparticular binary values may be different than the example above.Furthermore, in other systems, an individual memory component may have aconfiguration in which the number of selectable states may be more thantwo.

For a PCM cell, heat of a sufficient amount may be employed to changestate and may be achieved by generating a current and/or voltage pulseto be utilized with an electrode, such as bottom electrode 130, in amanner to affect a proximate PCM cell, such as 120, in an embodiment. Inthe embodiment illustrated 130 is in direct physical contact with cell120, for example. Of course, in one or more example embodiments, memoryarrays may comprise one or more technologies other than PCM, such asresistive memory technologies and/or other types of memory. Therefore,claimed subject matter is not limited in scope in this respect.

In an example embodiment, heat sufficient to change state of a PCM cell,such as 120, may be produced, for example, in connection with anelectrode, such as bottom electrode 130, due at least in part to currentflowing through the electrode. Heat may, as a result, also be generatedto affect the proximate PCM cell. In an embodiment, for example, acurrent may flow through an electrode, such as bottom electrode 130, andthrough a PCM cell, such as 120, at least in part as a result of avoltage across electrodes, such as electrically conductive electrode 140and top electrode 110, for example. In an embodiment, an amount of heatgenerated may depend, at least in part, on one or more characteristicsof an electrode, such as bottom electrode 130, one or morecharacteristics of a PCM cell, such as 120, and/or on an amount ofvoltage across the electrodes, such as a bottom electrode, such as 130,a top electrode, such as 110, and/or a PCM cell, such as 120, forexample.

In an embodiment, an amount of current to flow through an electrode,such as bottom electrode 130, and through a PCM cell, such as 120, maydepend at least in part on a resistance of an electrode, such as bottomelectrode 130, and/or of a PCM cell, such as 120. For example, anexpression for a measurable resistance of an electrode, such as bottomelectrode 130, and a PCM cell, such as 120, having a series arrangement,may comprise:

R _(M) =R _(SC) +R _(BE)   (1)

wherein R_(M) represents a measurable series resistance, wherein R_(SC)comprises a resistance of a PCM cell, such as 120, and wherein R_(BE)comprises a resistance of an electrode, such as bottom electrode 130. Inan embodiment, a PCM cell, such as 120, for example, may exhibitdifferent resistance characteristics depending at least in part onwhether the cell is programmed to a more conductive, set state or to amore resistive, reset state, as a result of a set or reset state of thememory material, for example.

A memory device, in an embodiment, may be considered to be capable ofdetecting a state of a particular PCM cell, such as PCM cell 120, basedat least in part on a ratio of a measurable resistance of the particularcell in a reset state to a measurable resistance of the particular cellin a set state, although, of course, other measures may be employed. Aratio may be expressed as:

$\begin{matrix}{{R_{off}/R_{on}}{wherein}} & (2) \\{{R_{off} = {R_{reset} + R_{BE}}}{and}} & (3) \\{{R_{on} = {R_{set} + R_{BE}}}{yielding}} & (4) \\\frac{R_{reset} + R_{BE}}{R_{set} + R_{BE}} & (5)\end{matrix}$

wherein R_(set) comprises a resistance of a PCM cell, such as 120, in aset state, wherein R_(reset) comprises a resistance of a PCM cell, suchas 120, in a reset state, and wherein R_(BE) comprises a resistance ofan electrode, such as bottom electrode 130.

As may be seen in expression (5) above, if a resistance characteristicfor an electrode, such as bottom electrode 130, in a PCM cell, such asPCM cell 120, remains approximately constant, resistance values for aPCM cell, such as storage 120, in a more conductive, set state and in amore resistive, reset state may affect the value of the ratio.Therefore, the ratio may be considered to reflect the ability to discernone state from another for a PCM cell, such as 120.

Additionally, in an embodiment, sufficient heat to change state of a PCMcell, such as to program it, may be achieved under a condition of areduced programming voltage and/or current if resistivity of anelectrode, such as bottom electrode 130, were increased. For example, ifresistivity were increased, sufficient heat may be generated using lesspower, such as a lower signal value level of voltage and/or current.However, an increase in resistivity of an electrode, such as bottomelectrode 130, may result in an on/off ratio being closer to unity thana situation involving lower resistivity. If this occurs, one potentialrisk may be that measurable resistance of a PCM cell in a set state maybecome more similar to measurable resistance of a PCM cell in a resetstate. This may potentially result in a reduction in an ability tosufficiently discern a set state from a reset state, for example, and/orvice-versa.

However, some embodiments in accordance with claimed subject matter maysatisfactorily address a situation such as this if resistivity werecapable of increasing in an environment of increasing heat, butotherwise did not increase and/or did not increase as much for anambient temperature environment, such as around room temperature, forexample. In an embodiment, an electrode, such as bottom electrode 130,for example may comprise a sufficiently electrically conductive materialso as to provide a relatively large positive temperature coefficient ofresistance, providing a resistivity that increases with an increase intemperature. In an embodiment, for example, an electrode, such as bottomelectrode 130, may have a smaller resistance at room temperature, thanat a more elevated temperature including, for example, a temperature atwhich memory material for a PCM cell may melt. In this manner, anelectrode, such as bottom electrode 130, may have a smaller resistanceat room temperature that may provide for a PCM cell on/off resistanceratio that may permit a sufficiently different resistivity so thatadequate determination of a state of a particular PCM cell is possible;nonetheless, a PCM cell may also have a relatively higher resistance ata relatively higher temperature, such as a temperature sufficient tomelt memory material of a PCM cell. Improved memory material heatingefficiency may allow for a reduction in a voltage and/or current signalvalue level. In an embodiment, an electrode, such as bottom electrode130, may comprise B_(a)T_(i)O₃, for example, although claimed subjectmatter is not limited in scope in this respect.

FIG. 2 is a plot of example resistivity against temperature forB_(a)T_(i)O₃, for example, that may comprise a material to be employedas an electrode for a PCM cell. FIG. 2 illustrates an example of amaterial providing a sufficiently large positive temperature coefficientof resistance (TCR) material to be utilized in an electrode, such asbottom electrode 130, in a PCM cell, such as PCM cell 120, for anembodiment. In an embodiment, bottom electrode 130 may compriseB_(a)T_(i)O₃, for example. Of course, other embodiments may utilizeother electrically conductive materials to provide a sufficiently largepositive TCR. As used herein, the term “sufficiently large positivetemperature coefficient of resistance” includes a positive temperaturecoefficient of resistance of approximately 0.01 or greater. In anembodiment, a material, such as B_(a)T_(i)O₃, for example, may have apositive TCR of approximately 0.05, although claimed subject matter isnot limited in this respect. Furthermore, it is noted that somematerials may exhibit a sufficiently large TCR while also exhibitingnon-linear behavior as a function of increasing temperature, forexample. A non-linear TCR that exhibits a sufficiently large positivetemperature coefficient of resistance may, for example, exhibitapproximately 0.01 or greater on average over a relevant range oftemperatures, such as, for example, from approximately 120° C. toapproximately 200° C. or greater.

As depicted in FIG. 2, an example curve 210 may correspond to aB_(a)T_(i)O₃ material, for example, having a lower level 220 ofresistivity at a temperature range of approximately less than 120° C.,and having a higher level 230 of resistivity at a temperature range ofapproximately greater than 200° C. For the example depicted in FIG. 2,resistivity increases substantially rapidly and substantially linearlyin a temperature range of approximately 120° C. and 200° C. Of course,characteristics depicted in FIG. 2 are merely examples, and otherembodiments may utilize materials that are adequate havingcharacteristics that differ from those depicted in FIG. 2.

TABLE 1 Example Materials with positive temperature coefficient ofresistance Reset Reset Resistivity Voltage Current Material (Ω · m) TCR(V) (mA) R_(reset) (Ω) R_(set) (Ω) V₂0₃ 1.00E−05 .01 1.05 468 7.38E+051009 Doped - 1.00E−05 0.05 1.10 314 8.03E+05 1008 B_(a)T_(i)O₃

Table 1 provides example characteristics for example materials thatexhibit sufficiently large positive TCR to be utilized, for example, inan electrode. For the material B_(a)T_(i)O₃, for example, an approximateTCR of 0.05 is exhibited, along with an approximate resistivity of1.00E−05Ω·m at room temperature. For an example embodiment of a PCM cellutilizing a bottom electrode comprising B_(a)T_(i)O₃, a reset voltagesignal value level of approximately 1.10V and a reset current signalvalue level of approximately 314 mA may be employed. Also, in anembodiment, a value level for R_(reset) may be estimated as 803 kΩ and avalue level for R_(set) may be estimated as 100Ω. Of course, valuelevels from Table 1 are merely examples, and claimed subject matter isnot limited in these respects.

As indicated previously, Table 1 provides an estimated value level for

R_(reset) of 803 kΩ and an estimated value level for R_(set) of 1008Ω.It may be noted that the example value level for R_(reset) for anexample embodiment of a PCM cell is several orders of magnitude greaterthan the example value level for R_(set). In an embodiment, a differencebetween R_(reset) and R_(set) may be attributable at least in part to asufficiently large positive TCR for a material of an electrode, such asbottom electrode 130, of an example PCM cell, such as PCM cell 120. Alsoin an embodiment, by utilizing a material with a sufficiently largepositive TCR for an electrode, such as bottom electrode 130, in a PCMcell, bottom electrode 130 may have a lower resistance at approximatelyroom temperature, such as at a temperature at which a state of PCM cell120 may be sensed.

Referring to expressions (2) through (5) above, note again that a lowerresistance in an electrode, such as bottom electrode 130, may have abeneficial affect on an on/off resistance ratio, thereby increasing alikelihood of being able to sufficiently discern a state of a particularPCM cell, such as PCM cell 120, in an embodiment. Additionally, a higherresistivity value for an electrode, such as bottom electrode 130, mayresult in an increase in heat generation efficiency for a PCM cell, suchas PCM cell 120, in an embodiment. An increase in heat generationefficiency may allow for a reduction in programming voltage and/orcurrent, for example, in an embodiment. Additionally, an increase inheat generation efficiency may allow for a reduction in bottom electrodesize, for example.

FIG. 3 is an illustration depicting an isometric view of an exampleapparatus 300, including an example PCM cell 320, according to anembodiment. In an embodiment, a PCM cell, such as PCM cell 320, maycomprise an electrode, such at top electrode 310, a memory cell, such as320, and an electrode, such as bottom electrode 330, for example. Also,in an embodiment, a PCM cell, such as PCM cell 320, may comprise anelectrically conductive component 340. In an embodiment, a PCM cell,such as PCM cell 320, may comprise one or more aspects that are similarto corresponding aspects of an example PCM cell, such as PCM cell 120,described above. In an embodiment, an electrically conductive component,such as an electrically conductive component 340, may comprise asufficiently electrically conductive material, such as polysilicon,carbon, and/or metallic material, such as tungsten, titanium nitride,and/or titanium aluminum nitride, for example, for use in a memorydevice. Also in an embodiment, top electrode 310 may comprise asufficiently electrically conductive material, such as polysilicon,carbon, and/or metallic material, such as tungsten, titanium nitride,and/or titanium aluminum nitride, for example, for use in a memorydevice, although again claimed subject matter is not limited in scope inthese respects. A memory cell, such as PCM cell 320, may comprise amemory material, such as a chalcogenide glass material, for example.

Additionally, in an embodiment, an electrode, such as bottom electrode330, may comprise a narrow component having wall-type shape, such as maybe manufactured at least in part by conformally depositing a materialhaving a sufficiently large positive TCR, such as B_(a)T_(i)O₃, forexample, over and/or on an approximately vertical wall of a trenchpositioned in a dielectric material. In an embodiment, a thickness of aconformal deposition of a material with a sufficiently large positiveTCR on a trench wall may affect, at least in part, a dimension of anelectrode, such as bottom electrode 330. Of course, embodiments inaccordance with claimed subject matter are not limited to any particularmanufacturing techniques.

Also depicted in FIG. 3 is a region 325 within PCM cell 320. In anembodiment, a portion of a PCM cell, such as PCM cell 320, may melt as aresult of sufficient heat and/or may change state with utilization ofsufficient heat. In FIG. 3, region 325 is meant to depict an approximateregion within PCM cell 320 that may experience a significant enoughincrease in heat to affect a change in state of a memory material withinregion 325. In an embodiment, a material with relatively highresistivity at relatively high temperature, such as at temperaturessufficient to melt at least a portion of a PCM cell, such as cell 320,may provide focused heat due at least in part to improved efficiency inheat generation provided by a material, such as B_(a)T_(i)O₃, forexample. A region within a PCM cell, such as PCM cell 320, may reduce alikelihood of thermal cross-talk with an immediately adjacent PCM cellas a result. Additionally, in an embodiment, utilization of a materialwith a relatively high resistivity at relatively high temperatures, suchas at temperatures sufficient to melt at least a portion of a PCM cellmay result in decreased heat loss through an electrode, such as bottomelectrode 330, for example, since heat may be conducted away from a PCMcell more slowly for materials exhibiting a sufficiently high TCR. Areduction in operating temperature may also result, in an embodiment,potentially providing improved memory device reliability.

FIG. 4 is an illustration depicting an isometric view of an exampleapparatus 400, including an example PCM cell 420, according to anembodiment. In an embodiment, a PCM cell, such as PCM cell 420, maycomprise an electrode, such at top electrode 410, a memory cell, such as420, and an electrode, such as bottom electrode 430, for example. Also,in an embodiment, a PCM cell, such as PCM cell 420, may comprise anelectrically conductive component 440. In an embodiment, a PCM cell,such as PCM cell 420, may comprise one or more aspects that are similarto corresponding aspects of example PCM cells, such as PCM cells 120and/or 320, described above. In an embodiment, an electricallyconductive component, such as an electrically conductive component 440,may comprise a sufficiently electrically conductive material, such aspolysilicon, carbon, and/or metallic material, such as tungsten,titanium nitride, and/or titanium aluminum nitride, for example, for usein a memory device. Also in an embodiment, top electrode 410 maycomprise a sufficiently electrically conductive material, such aspolysilicon, carbon, and/or metallic material, such as tungsten,titanium nitride, and/or titanium aluminum nitride, for example, for usein a memory device, although again claimed subject matter is not limitedin scope in these respects. A memory cell, such as PCM cell 420, maycomprise a memory material, such as, a chalcogenide glass material, forexample.

Further, in an embodiment, PCM cell 420 may comprise a hybrid-typebottom electrode, including a sufficiently large positive TCR portion435, and another portion 430. In an embodiment, portion 435 may compriseB_(a)T_(i)O₃, for example. Also in an embodiment, portion 430 maycomprise TiN, for example. Also depicted in FIG. 4 is a region 425within PCM cell 420. In an embodiment, region 425 is meant to depict anapproximate region within PCM cell 420 that may experience a significantenough increase in heat to affect a change in state of memory materialwithin region 425. In an embodiment, a material utilized for portion 435with a relatively high resistivity at higher temperatures, includingtemperatures sufficient to melt at least a portion of a PCM cell, suchas 420, may provide relatively focused heat to region 425 due at leastin part to improved efficiency in heat generation provided by amaterial, such as B_(a)T_(i)O₃, for example, having a sufficiently largepositive TCR. Region 425 within a PCM cell, such as PCM cell 420, mayprovide one or more potential benefits, including a reduced likelihoodof thermal cross-talk with immediately adjacent PCM cells, a decrease inheat loss through an electrode, such as bottom electrode portion 435,and/or a reduction in operating temperature that may result in improvedmemory device reliability, among others.

Although example embodiments are described herein with an example shapefor electrode 435, claimed subject matter is not limited in scope inthese respects. For example, embodiments are possible utilizing a shapefor electrode 435 similar to that depicted in FIG. 3 for bottomelectrode 330, although again, claimed subject matter is not limited inscope in this respect.

Additionally, other embodiments are possible with various shapes andconfigurations for PCM cells, such as PCM cell 420. For example, in anembodiment, for example as depicted in FIG. 5 discussed below, a PCMcell may comprise a confined cell structure, although again, claimedsubject matter is not limited in this respect.

FIG. 5 is an illustration depicting an isometric view of an exampleapparatus 500 including an example PCM cell 520, according to anembodiment. PCM cell 520 may comprise a confined cell structure, in anembodiment. Also, in an embodiment, an apparatus, such as apparatus 500,may comprise an electrode, such as top electrode 510, and an electrode,such as bottom electrode 530, for example. Also, in an embodiment,apparatus 500 may comprise an electrically conductive component 540. Inan embodiment, a PCM cell, such as PCM cell 520, may comprise one ormore aspects that are similar to corresponding aspects of example PCMcells, such as PCM cells 120 and/or 320, described above. In anembodiment, an electrically conductive component, such as anelectrically conductive component 540, may comprise a sufficientlyelectrically conductive material, such as polysilicon, carbon, and/ormetallic material, such as tungsten, titanium nitride, and/or titaniumaluminum nitride, for example, for use in a memory device. Also in anembodiment, top electrode 510 may comprise a sufficiently electricallyconductive material, such as polysilicon, carbon, and/or metallicmaterial, such as tungsten, titanium nitride, and/or titanium aluminumnitride, for example, for use in a memory device, although again claimedsubject matter is not limited in scope in these respects. A memory cell,such as PCM cell 520, may comprise a phase change material, such as, achalcogenide glass material, for example.

Further, in an embodiment, PCM cell 520 may comprise a hybrid-typebottom electrode, including a sufficiently large positive TCR portion535, and another portion 530. In an embodiment, portion 535 may compriseB_(a)T_(i)O₃, for example. Also in an embodiment, portion 530 maycomprise TiN, for example. Also depicted in FIG. 5 is a region 525within PCM cell 520. In an embodiment, region 525 is meant to depict anapproximate region within PCM cell 520 that may experience a significantenough increase in heat to affect a change in state of phase changematerial within region 525. In an embodiment, a material utilized forportion 535 with a relatively high resistivity at higher temperatures,including temperatures sufficient to melt at least a portion of a PCMcell 520 may provide relatively focused heat to region 525 due at leastin part to improved efficiency in heat generation provided by amaterial, such as B_(a)T_(i)O₃, for example, having a sufficiently largepositive TCR. Region 525 within PCM cell 520, may provide one or morepotential benefits, including a reduced likelihood of thermal cross-talkwith immediately adjacent PCM cells, a decrease in heat loss through anelectrode, such as bottom electrode portion 535, and/or a reduction inoperating temperature that may result in improved memory devicereliability, among others.

Although example embodiments are described herein as utilizingB_(a)T_(i)O₃, for electrodes, such as bottom electrodes 130, 330, 430,and/or 530, other embodiments may utilize other materials havingcharacteristics including a sufficiently large positive TCR. Severaladditional example materials are listed, although the list is notintended to be exhaustive, and claimed subject matter is not limited tothis particular example.

BaTiO₃-based compounds (BaSrTi3O, BaPbTiO3 . . . )

Mn-doped Ba_(0.8)Sr_(0.2)TiO3

(Ba_(0.996)Y_(0.004))TiO3 and (Ba_(0.746)Ca_(0.1)Sr_(0.15)Y_(0.004))TiO3

(Ba_(0.85)Pb_(0.15))TiO3

V2O3 based compound

ZnO—TiO₂—NiO ceramic

La2/3Ca1/3MnO₃

SnO2+2CoO and SnO2+Cr2O3 ceramics

Pb(Fe_(1/2)N_(1/2))O₃

MoSi_(x), TCR(3.1-3.9)*10⁻³ K⁻¹

FIG. 6 is a schematic block diagram depicting an example system 600including an example PCM device 620. In an embodiment, PCM device 620may comprise a storage area 622 including an array of PCM cells, such asin accordance with one or more examples. PCM device 620 may, in anexample embodiment, be coupled to a processor 610 by way of aninterconnect 615.

PCM device 620 in an embodiment may comprise a control unit 626.Additionally, storage area 622 may store instructions 624 that mayinclude one or more applications that may be executed by processor 610,according with an embodiment. Processor 610 may transmit a memory accesscommand to PCM device 620, for example. Control unit 626 may access oneor more memory cells of storage area 622 at least in part in response toreceiving the memory access command from processor 610, according to anembodiment. Of course, computing platform 600 is merely one example of asystem implemented in accordance with claimed subject matter, and thescope of claimed subject matter is not limited in these respects.

The term “computing platform” as used herein refers to a system and/or adevice that includes the ability to process and/or store data in theform of signals and/or states. Thus, a computing platform, in thiscontext, may comprise hardware, software, firmware or any combinationthereof (other than software per se). Computing platform 600, asdepicted in FIG. 6, is merely one such example, and the scope of claimedsubject matter is not limited to this particular example. For one ormore embodiments, a computing platform may comprise any of a wide rangeof digital electronic devices, including, but not limited to, personaldesktop or notebook computers, high-definition televisions, digitalversatile disc (DVD) players and/or recorders, game consoles, satellitetelevision receivers, cellular telephones, personal digital assistants,mobile audio and/or video playback and/or recording devices, or anycombination of the above. Further, unless specifically stated otherwise,a process as described herein, with reference to flow diagrams and/orotherwise, may also be executed and/or controlled, in whole or in part,by a computing platform.

The terms, “and”, “or”, and “and/or” as used herein may include avariety of meanings that also are expected to depend at least in partupon the context in which such terms are used. Typically, “or” if usedto associate a list, such as A, B or C, is intended to mean A, B, and C,here used in the inclusive sense, as well as A, B or C, here used in theexclusive sense. In addition, the term “one or more” as used herein maybe used to describe any feature, structure, and/or characteristic in thesingular and/or may be used to describe a plurality or some othercombination of features, structures and/or characteristics. Though, itshould be noted that this is merely an illustrative example and claimedsubject matter is not limited to this example.

Methodologies described herein may be implemented by various techniquesdepending, at least in part, on applications according to particularfeatures and/or examples. For example, methodologies may be implementedin hardware, firmware, or combinations thereof, along with software(other than software per se). In a hardware implementation, for example,a processing unit may be implemented within one or more applicationspecific integrated circuits (ASICs), digital signal processors (DSPs),digital signal processing devices (DSPDs), programmable logic devices(PLDs), field programmable gate arrays (FPGAs), processors, controllers,micro-controllers, microprocessors, electronic devices, other deviceunits designed to perform function described herein, or combinationsthereof.

In the preceding detailed description, numerous specific details havebeen set forth to provide a thorough understanding of claimed subjectmatter. However, it will be understood by those skilled in the art thatclaimed subject matter may be practiced without these specific details.In other instances, methods and/or apparatuses that would be known byone of ordinary skill have not been described in detail so as not toobscure claimed subject matter.

Some portions of the preceding detailed description have been presentedin terms of logic, algorithms and/or symbolic representations ofoperations on binary states stored within a memory of a specificapparatus or special purpose computing device or platform. In thecontext of this particular specification, the term specific apparatus orthe like includes a general purpose computing device, such as generalpurpose computer, once it is programmed to perform particular functionspursuant to instructions from program software. Algorithmic descriptionsand/or symbolic representations are examples of techniques used by thoseof ordinary skill in the signal processing and/or related arts to conveythe substance of their work to others skilled in the art. An algorithmis here, and generally, is considered to be a self-consistent sequenceof operations and/or similar signal processing leading to a desiredresult. In this context, operations and/or processing involve physicalmanipulation of physical quantities. Typically, although notnecessarily, such quantities may take the form of electrical and/ormagnetic signals and/or states capable of being stored, transferred,combined, compared or otherwise manipulated as electronic signals and/orstates representing information. It has proven convenient at times,principally for reasons of common usage, to refer to such signals and/orstates as bits, data, values, elements, symbols, characters, terms,numbers, numerals, information, and/or the like. It should beunderstood, however, that all of these or similar terms are to beassociated with appropriate physical quantities and are merelyconvenient labels. Unless specifically stated otherwise, as apparentfrom the following discussion, it is appreciated that throughout thisspecification discussions utilizing terms such as “processing,”“computing,” “calculating,” “determining”, “establishing”, “obtaining”,“identifying”, “selecting”, “generating”, and/or the like may refer toactions and/or processes of a specific apparatus, such as a specialpurpose computer and/or a similar special purpose computing device. Inthe context of this specification, therefore, a special purpose computerand/or a similar special purpose computing device is capable ofmanipulating and/or transforming signals and/or states, typicallyrepresented as physical electronic and/or magnetic quantities withinmemories, registers, and/or other information storage devices,transmission devices, and/or display devices of the special purposecomputer and/or similar special purpose computing device. In the contextof this particular patent application, the term “specific apparatus” mayinclude a general purpose computing device, such as a general purposecomputer, once it is programmed to perform particular functions pursuantto instructions from program software.

In some circumstances, operation of a memory device, such as a change instate from a binary one to a binary zero or vice-versa, for example, maycomprise a transformation, such as a physical transformation. Withparticular types of memory devices, such a physical transformation maycomprise a physical transformation of an article to a different state orthing. For example, but without limitation, for some types of memorydevices, a change in state may involve an accumulation and/or storage ofcharge or a release of stored charge. Likewise, in other memory devices,a change of state may comprise a physical change, such as atransformation in magnetic orientation and/or a physical change ortransformation in molecular structure, such as from crystalline toamorphous or vice-versa. In still other memory devices, a change inphysical state may involve quantum mechanical phenomena, such as,superposition, entanglement, and/or the like, which may involve quantumbits (qubits), for example. The foregoing is not intended to be anexhaustive list of all examples in which a change in state form a binaryone to a binary zero or vice-versa in a memory device may comprise atransformation, such as a physical transformation. Rather, the foregoingis intended as illustrative examples.

A computer-readable (storage) medium typically may be non-transitoryand/or comprise a non-transitory device. In this context, anon-transitory storage medium may include a device that is tangible,meaning that the device has a concrete physical form, although thedevice may change its physical state. Thus, for example, non-transitoryrefers to a device remaining tangible despite a change in state.

While there has been illustrated and/or described what are presentlyconsidered to be example features, it will be understood by thoseskilled in the art that various other modifications may be made and/orequivalents may be substituted, without departing from claimed subjectmatter. Additionally, many modifications may be made to adapt aparticular situation to the teachings of claimed subject matter withoutdeparting from the central concept(s) described herein.

Therefore, it is intended that claimed subject matter not be limited tothe particular examples disclosed, but that such claimed subject mattermay also include all aspects falling within the scope of appended claimsand/or equivalents thereof.

1. A memory device, comprising: a phase change memory (PCM) cellpositioned between electrodes, wherein a portion of one of theelectrodes comprises a material exhibiting a sufficiently large positivetemperature coefficient of resistance (TCR).
 2. The memory device ofclaim 1, wherein the portion of one of the electrodes comprises amaterial having a sufficiently large positive TCR of approximately 0.01and/or greater.
 3. The memory device of claim 1, wherein the portion ofone of the electrodes comprises a material having a sufficiently largepositive TCR of approximately 0.05 and/or greater
 4. The memory deviceof claim 1, wherein the one of the electrodes comprises a materialdeposited on an approximately vertical wall of a trench positioned in adielectric material.
 5. The memory device of claim 1, wherein theportion of one of the electrodes comprises a first portion having asufficiently large TCR and a second portion, wherein the first portioncontacts the PCM cell and wherein the second portion does not contactthe PCM cell.
 6. The memory device of claim 1, wherein the PCM cellcomprises a chalcogenide glass material.
 7. The memory device of claim1, wherein the portion of the one of the electrodes comprisesB_(a)T_(i)O₃.
 8. The memory device of claim 1, wherein the portion ofone of the electrodes contacts the PCM cell.
 9. A method, comprising:generating a voltage across electrodes to induce a current through theelectrodes and through a PCM cell contacting the electrodes, wherein aresistance characteristic of a portion of one of the electrodesincreases with an increase in temperature of the portion.
 10. The methodof claim 9, wherein the generating the voltage comprises generating aprogramming voltage across the electrodes.
 11. The method of claim 10,wherein the generating the programming voltage comprises melting aregion of the PCM cell contacting the portion.
 12. The method of claim11, wherein melting the region contacting the portion comprises heatingthe region by generating the programming voltage.
 13. The method ofclaim 12, wherein the resistance characteristic of the portion comprisesan increased resistance in response to the heating of the region. 14.The method of claim 13, further comprising: generating a voltage acrossthe electrodes to sense a state of the region.
 15. The method of claim14, wherein the generating a voltage across the electrodes to sense astate of the PCM cell comprises the portion having a reduced resistanceas compared to the increased resistance in response to the heating ofthe region.
 16. A memory device, comprising: an array of phase changememory (PCM) cells comprising one or more PCM cells electricallyconnected between electrodes, wherein one of the electrodes comprises asubstantially electrically conductive material having a lowerresistivity and wherein another of the electrodes comprises a materialhaving a resistivity that substantially increases with a correspondingincrease in temperature.
 17. The memory device of claim 16, wherein thematerial comprise a sufficiently electrically conductive material. 18.The memory device of claim 16, further comprising an electricallyconductive component coupled to the another of the electrodes, whereinthe electrically conductive component comprises a metal material. 19.The memory device of claim 16, wherein the another of the electrodescomprises a first and a second portion, wherein the first portioncomprises a material having a relatively large positive temperaturecoefficient of resistance (TCR)
 20. The memory device of claim 18,wherein the second portion comprises a material having a smaller TCR ascompared to the first portion.